Grid electrode



United States Patent 3,141,991 GRID ELECTRODE Hendrikus- Johannes Marie Van T01 and Ernst Sigmund Den Dulk, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Original application May 29, 1957, Ser. No. 662,378, now Patent No. 3,054,430, dated Sept. 18, 1962. Divided and this application Aug. 12, 1960, Ser. No. 54,559 Claims priority, application-Netherlands June 13, 1956 S'Claims. (Cl. 313-350) This invention relates to grid structures for electron discharge tubes and to a method of making them.

This application is a division of application Serial Number 662,378, filed'M'ay 29, 1957, now US. Patent 3,054,- 430.

It has been found that grid structures for vacuum tubes and particularly for special vacuum tubes, such as those in which long life and reliability are of prime importance, can be made with greater uniformity and improved reliability of operation if the grid wires are exceedingly thin so as to be incapable of self support and are wound on relatively sturdy side, or stay, rods that also determine the spacing of the wires from ether elements of the tube. Grids of this type have been formed heretofore by winding very fine wire on a structure in the form of an open rectangular frame and sealing the wires to the frame at each point of contact, i.e., twice per turn.

According to the invention a long pair of stay rods is connected by cross-bars in a ladder-like structure with alternate cross-bars being attached to opposite sides of the structure and extending out beyond one of the stay rods so that the wire can be hooked into the notch between the rod and the cross-bar. The wire may then be hooked into the notch between the rod and the first cross-bar, wound in a number of turns to the second cross-bar on the opposite side of the stay rods, hooked into the notch between the second cross-bar and the rod, led along the rod to the third cross-bar and hooked into the notch between the latter cross-bar and the stay rod and so on, repetitively for the length of the rods. In this way the resultant structure is a succession of grid windings, each bounded at each end by a cross-bar and separated from one another by spaces in which there are no windings. Instead of soldering the wire to the stay rods at each point of contact, the fine wire is attached only in the section of the rod between adjacent wound sections. Attachment may be made by welding a small metal strip lengthwise on the stay rod in the interval between adjacent wound sections so as to press the fine wire against the stay rod and hold it in place. Alternatively, and particularly if the stay rods are made of molybdenum and the fine wire is made of tungsten, the wire may be pressed into the stay rods in the interval between wound sections.

The primary object of the invention is to provide improved grid structures and an easier method of forming them.

Other objects will be apparent from the following specification together with the drawings in which FIG. 1 shows a section of a ladder-like structure including portions of two wound sections and the interval between;

FIG. 2 shows a top view of the structure in FIG. 1;

FIG. 3 shows an end cross-sectional view of the structure in FIG. 1;

FIG. 4 shows the structure of FIG. 3 positioned in a press;

FIG. 5 shows an alternate embodiment of the structure shown in FIG. 2; and

FIG. 6 shows a cross-sectional end view of the alternate embodiment in FIG. 5.

For convenience FIG. 1 shows only a small portion of ice grid structures formed according to the invention at the stage of formation immediately preceding the step of cutting the formation into individual gridstructures. In FIG. 1 the stay rods 1 and 2 are only short fragments of their actual length. These rods are connectedtogether in accurately spaced relation by' cross-bars 3 and 4 which are attached to opposite sides of therods 1 and 2 by any convenient means, such as by spot welding. Portions of two grid structures 5 are shown,-one to the left of cross-bar 3 and the other to the right of cross-bar 4. These are spaced apart by the interval 6 which is the interval in which the rods 1 and 2 will eventually be cut to separate the grid structures 5 from each other.

Thegrid structures5 are formed by windingvery fine wire 7, for example wire having a'diameter of the order of 7.5 microns, in a series of closely spaced turns. Assuming for the purpose of illustration that the wire 7 is wound from left to right, the last turn in the left hand section 5 will bring the wire 7 up against the cross-bar 3 which extends beyond the stay rod 1 on the same side thereof as the last part of the turn of wire 7 so that wire 7 can be fitted into a notch between the cross-bar 3 and the stay rod 1 and pulled practically directly along the stay rod 1 to the cross-bar 4 which is on the opposite side of cross-bar 3. The wire 7 then fits into a notch between cross-bar 4 and rod 1 and is wound in another series of closely spaced turns to make the right hand section 5. Any convenient number of sections 5 can be formed in this way at one winding, and the spacing between adjacent turns may be varied as desired.

It is necessary to wind the wire 7 with relatively high tension so that subsequent heat treatment during the formation of the tube will not cause the wire to go slack in the structures 5. It has been found that the tension should be of the order of 60% of the tensile strength of the wire. For example, grids made of tungsten wire having a diameter of 10 microns have been wound using a winding tension of 15 to 17 grams which is about 50 to 60% of the 30 to 34 gram tensile strength of the wire. After annealing, the wire in sections 5 of grids so formed was found to be reduced to about 1.5 to 3 grams, which, however, is still suflicient to cause the wire in sections 5 of grids so formed was found to be reduced to about 1.5 3 grams, which, however, is still suflicient to cause the wire in sections 5 to remain taut, thereby maintaining the spacing between adjacent turns of the wire and also between elements in the tube, such as the cathode and anode.

FIGS. 2 and 3 show the way the wire 7 crosses over the stay rod 1 in the region 8 and the dotted rectangle 9 indicates the region in which the wire may be pressed into the stay rod 1 to keep the wire from becoming unwound when the individual grid structures are cut apart.

FIG. 4 shows an example of a press including an anvil 10 and a die 11 that moves in the direction of the arrow to press the wire sections 8 into rod 1. After the step of pressing has been completed, the individual grid structures may be cut apart, for example by cutting the rods 1 and 2 half way between the cross-bars 3 and 4 (FIG. 1).

FIGS. 5 and 6 show an alternate structure in which additional cross-bars are used so as to obtain a symmetrical structure. In this case the stay rods 12 and 13 are held firmly by means of cross-bars 14-17 so that there is no tendency for the stay rods 12 and 13 to twist and thereby alter the spacing between them under the tension of the winding of the grid wire.

FIGS. 5 and 6 also illustrate a difierent way of permanently securing the wire to the stay rods. In this case a metal strip, for example, of nickel, is placed lengthwise of the stay rod 12 in the region between the cross-bars 14, 15 and the cross-bars 16, 17 and spot welded at several points as indicated by the xs. Again the grid structures may be separated by cutting the stay rods somewhere between cross-bars 14, 15 and cross-bars 16, 17.

As an illustration of a typical embodiment of the invention, grid structures 5 have been made as shown in FIG. 1 with a wound length of 7.5 mm. and a spacing 6 of about 3.4 mm., using 7.5 micron wire wound with a pitch of 70 microns on stay rods 8 mm. in diameter and spaced apart by 3.2 mm.

Modifications of the embodiments shown may be made within the scope of the invention as defined by the following claims.

What is claimed is:

1. A grid electrode for an electron discharge tube comprising a pair of spaced stay-rods, a pair of cross-bar members placed cross-wise in spaced relationship over the stay rods, one end of each cross-bar member protruding from a stay-rod thereby forming a notch with the stayrod, a grid wire helically wound over the stay-rods between the cross-bar members, the end of said grid-wire passing between the cross-bar members and the stay-rods 4 in the notch therebetween and being secured to the stayrod outside the effective length of the grid electrode.

2. A grid electrode as claimed in claim 1 in which the wire has a diameter less than about 15 microns and is wound with a pitch which is less than 75 microns.

3. A grid electrode as claimed in claim 2 in which the stay-rods are molybdenum and the wire is tungsten.

4. A grid electrode as claimed in claim 1 in which wire is clamped between the stay-rod and a strip welded to the stay-rod outside the effective length of the grid electrode.

5. A grid electrode as claimed in claim 1 in which the wire is pressed into and thus secured to the stay-rod outside the elfective length of the grid electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,960, 621 Lane et al Nov. 15, 1960 FOREIGN PATENTS 1,082,995 France June 23, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 3 14l 991 July 21 1964 Hendrikus Johannes Marie Van T01 et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 24 for "ether" read other column 2 lines 43 to 45, strike out "of grids so formed was found to be reduced to about 1,5 3 grams which however is sti1l sufficient to cause the wire in sections 5"; column 3 line 2O for "end" read ends Signed and sealed this 24th day of November 19640 SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer 7 i Commissioner of Patents 

1. A GRID ELECTRODE FOR AN ELECTRON DISCHARGE TUBE COMPRISING A PAIR OF SPACED STAY-RODS, A PAIR OF CROSS-BAR MEMBERS PLACED CROSS-WISE IN SPACED RELATIONSHIP OVER THE STAY RODS, ONE END OF EACH CROSS-BAR MEMBER PROTRUDING FROM A STAY-ROD THEREBY FORMING A NOTCH WITH THE STAYROD, A GRID WIRE HELICALLY WOUND OVER THE STAY-RODS BETWEEN THE CROSS-BAR MEMBERS, THE END OF SAID GRID-WIRE PASSING BETWEEN THE CROSS-BAR MEMBERS AND THE STAY-RODS IN THE NOTCH THEREBETWEEN AND BEING SECURED TO THE STAYROD OUTSIDE THE EFFECTIVE LENGTH OF THE GRID ELECTRODE. 